The present invention relates to a process and to a device for controlling the regeneration of a system for collecting carbon-containing elements, such as a particle filter installed on a gaseous flow system, for example in an internal-combustion engine, by means of differential measurement of the fuel/air ratio of the gas at the boundaries of the filtering element.
The filtering means allow to collect the particles discharged at the exhaust of an internal-combustion engine with high filtering efficiencies of the order of 80%. The cordierite-based ceramic monolith marketed by the Corning company, the silicon carbide-based ceramic monolith marketed by the Ibiden company or cartridges with wound ceramic fibers can be mentioned by way of example.
The technical difficulty encountered when developping and installing particle filters lies in the fact that they must be periodically regenerated by combustion of the soot deposit in order to prevent clogging of the filtering element, which will penalize the engine efficiency and imperil the working order of the engine. This combustion sometimes occurs naturally when the temperature of the gas flowing through the filter reaches a sufficient level to initiate oxidation of the particles. However, the temperature levels encountered at the exhaust of Diesel engines for example remain, within a very wide operating range, much too low to allow initiation of the soot combustion. It is then necessary to implement actions allowing to initiate regeneration of the filter.
Many techniques have been developped to that effect. They can be based on changes in the engine running parameters, such as the EGR ratio, supercharging, the injection delay, throttling at the exhaust, throttling at the intake, they can be linked with the use of an oxidation catalyst placed upstream from the filtering element coupled with a post-injection, or they can involve an external energy supply to the exhaust gas or in the filter by means of resistors, burners, micro-waves, plasma, etc. It is then necessary to drive these various devices by means of an external control operated by the computer.
The criterion for initiating regeneration of the filtering element can be the back pressure variation or pressure drop measured at the boundaries of the filtering element, which can be correlated with its fouling level due to the soot, as described for example in patent FR-2,755,623 filed by the applicant. This detection process is very suitable under stabilized running conditions. Measurement of the back pressure also allows to detect the combustion of the soot accumulated in the filtering element because, under stabilized running conditions, it drops with the combustion of the carbon-containing deposit. However, the back pressure at the exhaust is subjected to great fluctuations when the engine conditions are not stabilized (temperature, air flow rate, etc.). This is the case for the engine of a vehicle that, under usual traffic conditions, very often works under transient conditions (acceleration, deceleration). Controlling the fouling level of a filtering element by means of this type of measurement is difficult in practice.
Initiation of the regeneration of the filtering element can also be controlled by measuring the resistor variation measured between points spaced out along the filtering element, a variation that is directly linked with the fouling level thereof as described for example in patent FR-2,760,531 filed by the applicant.
Regeneration of the filter can be facilitated by using additives in the fuel based, for example, on organometallic or rare-earth elements, that are found in the soot deposit and catalyse the oxidation of the soot, which leads to a fall in the combustion initation temperature for the carbon-containing deposit. Cerium, strontium, iron, etc., can be mentioned as examples of the most commonly used products. Using these elements allows to obtain regenerations at temperatures ranging between 200xc2x0 C. and 450xc2x0 C. according to the nature of the soot deposit. However, the temperatures encountered for example at the exhaust of supercharged Diesel engines can remain, for certain types of use such as urban traffic, insufficient for initiation of the combustion of soot. Implementation of specific strategies involving the various elements mentioned above becomes essential for the system to work properly. Various examples of use of these various techniques are described for example in the following patents: EP-913,559, JP-10,141,113, GB-2,261,613, EP-488,386 or DE-35,38,109.
Whatever the means used for initiating regeneration of the filtering element, it causes energy consumption. Good management of the system requires control of the regeneration stage. More precisely, detection of the filter regeneration start allows to define the moment when the means used for increasing the temperature of the gas can be stopped. Combustion of the soot can then be self-sustained because of the high exothermicity of the soot oxidation reaction. This notably leads to a limitation of the overconsumption of the engine linked with the implementation of the strategies for regenerating the filtering element.
The present invention allows very efficient control of the stage of regeneration of the filtering elements and of the operations required to clean them.
The process according to the invention allows to control the periodic regeneration of an element filtering particles that are carried along by a gaseous stream, through combustion of these particles. It is characterized in that it comprises detecting the variation in the oxygen concentration of the gaseous stream between at least a first point located upstream from the filtering element receiving the stream, in relation to the direction of flow thereof, and at least a second point located downstream from the first point, resulting from a triggered reaction of combustion of the particles accumulated in the filtering element, so as to adjust with precision the warming up time required for initiation of the combustion and therefore to limit the energy required as far as possible.
According to an embodiment, the process allows for example to control the periodic regeneration of a filtering element such as an exhaust silencer, intended to retain particles or soot carried along by a gaseous stream flowing out of an engine, by combustion of these particles. It is characterized in that it comprises detecting the variation in the fuel/air ratio of the exhaust gas between at least a first point located upstream from the filtering element in relation to the direction of flow and at least a second point located downstream therefrom, resulting from a reaction of combustion of the particles accumulated in the filtering element, initiated by a management element sensitive to the detected fuel/air ratio variation, so as to adjust with precision the warming up time required for initiation of the combustion.
In some cases, the process can comprise controlling the spontaneous regeneration of the filtering element or initiating an action on the engine running parameters in order to obtain a substantial exhaust gas temperature rise, or initiating heating means associated with the filtering element.
The device according to the invention allows to control the periodic regeneration of a filtering element that retains particles carried along by a gaseous flow, by combustion of these particles. It is characterized in that it comprises means for detecting the variation in the oxygen content of the gaseous stream between at least a first point located upstream from the filtering element receiving the stream, in relation to the direction of flow thereof, and at least a second point located downstream therefrom (preferably downstream from the filtering element), heating means intended to raise the temperature of the filtering element sufficiently to burn the particles, and management means connected to the detection means in order to adjust the warming up time required for initiation of the combustion, by acting on the heating means.
In an application to the control of the periodic regeneration of a filtering element that retains oxidable particles or soot carried along by a gaseous stream flowing out of a thermal engine, by combustion of these particles, the device comprises a first fuel/air ratio detector arranged at a first point located upstream from the filtering element in relation to the direction of flow and a second fuel/air ratio detector arranged at a second point located downstream from the first one (preferably downstream from the filtering element), in relation to the direction of flow of the gas, heating means intended to raise the temperature of the filtering element sufficiently to burn the particles, and a computer connected to the detection means so as to adjust the warming up time required for initiation of the combustion, by acting on the heating means, according to the fuel/air ratio variation of the exhaust gas between the first and the second detector.
The heating means can for example consist of the engine, the computer being programmed to modify the running parameters intended to raise the temperature of the exhaust gas, or they can be associated with the filtering element.